Progressive, or multifocal, lenses are well known and widely used especially by patients suffering from weak eyesight in both `reading` and `distance` visions, such as, for example, presbyopia. There is a certain number of standard progressive lenses produced by various manufacturers. As known in the, art, the main features characterizing each standard progressive lens are its optical power and distortions distribution within the lens, as clearly illustrated in FIGS. 1a and 1b, respectively. There is practically no way of eliminating or substantially reducing the distortions, because the progressive lens is typically formed with a certain `local cylinder` thereof.
Referring to FIG. 2, there is illustrated a final map of a standard progressive lens, generally designated 1, manufactured in accordance with prescribed parameters of optical powers required for a patient's `distance` and `reading` visions and cylinder parameters, if any. The lens 1 is formed with four main zones 2 to 5. The zone 2 is a far vision zone corresponding to the patient's `distance` vision, the zone 3 is a near vision zone corresponding to the patient's `reading` vision, the zone 4 is a zone of continuous focus, and the zone 5 is the zone of concentrated optical distortions, so-called `transition` zone. All the above features of the progressive lens are well known per se and, therefore, do not need to be described in more detail. Additionally, it is important to note that each standard lens is characterized by its `addition` value defined by a difference in powers in the far and near visions. As shown, the far vision zone 2 is surrounded by a free of distortions region which almost completely occupies the upper semicircular region of the lens. The near vision zone 3 is always spaced a certain preset distance from a major reference point (MRP) of the lens which is common for the lenses of a specific standard kind, wherein the MRP is defined as the point with zero prism and it approximately coincides with the geometrical center of the lens. Generally, the location of a center of the near vision zone 3 is mostly considered to be 16 mm below the MRP of the lens and 2 mm therefrom towards the center of the spectacles. This location is not agreed by all manufactures and there are standard lenses with different locations of reading zones relative to the MRP. As clearly shown in FIG. 2, an undistorted region around the near vision zone 3 is extremely narrow, which is typical for all progressive lenses.
The whole process of providing a patient with progressive lens spectacles generally includes the following stages:
1) determining for each eye of the patient first and second values of the optical power required for the patient's eyesight in `reading` vision and `distance` vision regions; PA1 2) selecting for each eye a lens of a suitable standard kind according to its `addition` value, and processing an inner side of the lens according to the prescribed first and second values of the optical power; and PA1 3) cutting and mounting the lens in the frame of the spectacles, previously chosen by the patient, in such a position that an inter pupillary distance of the patient for `distance` vision matches a distance between the far vision zones 2 of the pair of progressive lenses. PA1 (a) determination of the direction of a line of sight of the patient's eve at said reading vision, relative to the frame of the spectacles; and PA1 (b) positioning and orientation said progressive lens relative to said frame so as to ensure that said line of sight passes through said near vision zone of said progressive lens. PA1 determination of said distributions of optical power and optical distortions in said progressive lens; PA1 determination of the direction of a line of sight of the patient's eye for at least one of said visions, relative to the frame of the spectacles; and positioning and orienting said progressive lens relative to said frame so as to ensure that said line of sight passes through the respective vision zone of the progressive lens at a location thereon in which the optical power of the progressive lens is substantially of said respective value and in which said optical distortions are minimal. PA1 (i) a device for the determination of the direction of a line of sight of the patient's eye it said reading vision, relative to the frame of the spectacles, and PA1 (ii) a device for the positioning and the orienting of said progressive lens relative to said frame so as to ensure that said line of sight passes through said near vision zone of said progressive lens. PA1 a mapping device for the determination of the distributions of said optical power and of said optical distortions of said progressive lens; a means for determination of the direction of a line of sight of the patient's eye for at least one of said visions, relative to the frame of the spectacles; and PA1 a device for the positioning and the orienting of said progressive lens relative to said frame so as to ensure that said line of sight passes through the progressive lens at a location thereon in which the optical power is substantially of the respective value and in which the distortions are minimal.
The first stage is conventionally carried out by specialists, namely by a physician or a skilled optometrist. The second stage is carried out by a sophisticated producer. The third stage, which is not less critical for succeeding in adjusting the spectacles, is carried out by an optician whose capability suffers from certain serious limitations associated with the conventional approach and equipment he has at his disposal,
Each standard lens is usually available with markings specifically indicating the locations of the zones 2 and 3. Thus, as illustrated in FIG. 3, the optician determines an inter pupillary distance for the patient's `distance` vision and inputs the respective data, as well as the spectacles' frame parameters, i.e. its dimensions, into a so-called `edger` which is typically used for circumferential cutting of a lens so as to design a contour thereof suiting that of the frame. Upon detecting that the pupil location for the `distance` vision falls within the zone 2 marked on the lens, the optician operates the edger for cutting the lens.
It is often the case that such a complicated process of adjusting progressive lenses for a patients spectacles gives unsatisfactory results, and it is not an exaggeration to say that most patients feel uncomfortable with their new spectacles for a long time until the eyes `get accustomed` to the lenses and for considerable number of patients it never happens. One of the reasons for this is that the adjustment is, actually, solely based on `distance` vision parameters of the patient's eyesight, while that of the `reading` vision are completely ignored. It should be specifically noted that an inter pupillary distance for the reading vision has never been measured in the conventional approach for adjusting the progressive lenses for the patient's spectacles, since it was assumed that the above indicated relative location of the near vision zone 3 is suitable for all patients. However, the inter pupillary distance of the specific patient in the `reading` vision may not match the near field zone location of the standard lens. In such case there is an expectation that the patient will adapt himself to the lenses, but in many cases it never happens.